I'm on an M2 Mac mini, but I feel NO speed difference between the old and a new UI.
There is however a quite noticeable speed difference between the previous stable release
and the current 2023.1 stable release.
The startup time feels a few seconds faster, because the IDE becomes responsive earlier
in its boot process. See the "Earlier availability of IDE features on project opening" section
What I do notice and absolutely hate, how the new UI has a super thick gutter, which
I found no way to reduce to that level as it was in the old UI.
I usually have 2-3 code editor columns + the Cursive REPL tool window.
The extra gutter wastes about 1-2 character width per editor split. I could hardly fit
3x80 column width on 1080p resolution or 4x80 cols width on 2K resolution, so it's
it's very annoying that I'm losing 4-6 extra characters for "aesthetic" reasons...